The sport of golf has a long history and is enjoyed by many participants throughout the United States and the world. The sport is well known and need not be described in detail except as is necessary to describe the present invention. Briefly, a player strikes a golf ball with a golf club. The golf club includes a shaft gripped by the player ("golfer"), to which is attached a golf club head which strikes the ball. The portion of the head that strikes the ball is called the "face," which is a generally planar surface. The bottom perimeter of the golf club face (as defined when the club is used in its intended manner to strike the ball) is called the "sole." It is noted here that the golf clubs relevant to the present invention are all "distance" clubs, as opposed to "putters," which are used in a substantially different manner from distance clubs and which are not relevant to the present invention.
A phenomenon all too familiar to most recreational golfers and even professional golfers is the "slice," which is a description of the path of a golf ball that moves in an increasing curve away from a golfer in the direction the golfer is facing. While it is in some cases be desirable to slice the ball, a slice is much more commonly the result of flaws in the golfer's swing. Slicing the ball misdirects the ball from its intended trajectory, which can frustrate the golfer and prevent the golfer from obtaining a satisfactory score.
A slice is caused by a horizontally glancing blow of the club, which imparts spin. Such a glancing blow is influenced by the club face angle and by the swing path at the moment of impact. To avoid a slice, the face angle and the swing path should be at right angles at the absolute point of impact. However, because the club head carries the ball somewhat during and immediately after impact, there is a high likelihood of imparting a slicing horizontal spin.
A related phenomenon is the "hook," which is a description of the path of a golf ball that moves in a curve away from the direction the golfer is facing. Because of the swing path of a typical golfer, hooking is much less common than slicing. Like the slice, the hook is sometimes intended but it more often unintended, and can also prevent a golfer from achieving a good score. However, the difficulty of hooking the ball and its perceived aesthetics are such that sometimes a golfer will attempt to hook the ball, in a shot called a "draw." The ability to make a draw show is often a source of accomplishment to the golfer.
In addition to a horizontal spin that would cause a slice or hook, a struck golf ball generally also has a backspin, which is the spinning of the ball in a clockwise manner in relation to the vertical axis of the golfer, from the golfer's perspective. The spinning ball rises because of the Magnus Effect (as described in more detail herein), thus affecting the trajectory. More backspin results in a higher trajectory. Additionally, backspin aids in the ability to stop the ball on the green without excess roll.
A number of different golf clubs are used by a golfer depending upon the position of the ball on the course and its distance to the hole. Typical golf clubs are a set of "woods," a set of "irons" in the range of 1-9, and several of wedges. The difference between the clubs (within a class of clubs) are the "loft" of the golf head, which is the angle between the club head face and the axis of the shaft, and the length of the shaft. The higher lofted clubs typically have shorter shafts; the combination of high loft and a short shaft results in greater backspin.
A consequence of the longer shaft lengths of the lower lofted clubs is increased head speed. This is because such a club is swung in an arc of greater radius than a shorter club. The increased head spin increases the horizontal spin and exaggerates a slice (or a hook).
Presently, all commercially available clubs known to the inventor have grooves in the club face that are parallel to the club face sole. Such grooves increase the friction between the club face and the ball and therefore increase the spin imparted to the ball. While such grooves are useful for increasing backspin, they do not assist in imparting a desired horizontal spin that could correct for a hook or slice.
U.S. Pat. No. 5,785,610 of Birmingham (1998) describes a golf club having grooves in a what is a described as a "chevron" pattern. The chevron pattern grooves may serve to impart horizontal spin to the ball. However, the chevron pattern is not believed to be useful because it assumes that horizontal spin that is imparted on the ball is solely a function of the portion of the club face that the impacts the ball. It therefore has grooves of different angular slopes across the club face. It is believed that the chevron pattern is not effective in reducing slice, and further, even if grooves of different slope across the club face are used, the slopes should not be as shown in the Birmingham patent.
An understanding of the principles behind the present invention requires an understanding of the "Magnus Effect." This well understood effect is a particular manifestation of Bernoulli's theorem that fluid pressure decreases as fluid speed increases. This effect explains the "curve" of rotating balls such as baseballs and golf balls. Pressure differences develop in a fluid through which a spinning sphere moves. Greater pressure on the side where the airflow is slowed down forces the ball in the direction of the low-pressure region on the opposite side, where there is a relative increase in airflow.
Finally, it should be noted that while the principles on which the present invention is based are believed to be well understood, the effectiveness of the present invention has been verified through experiment and therefore the scope the invention should not be limited by the validity of any scientific theory.